Method of operating a laundry treating appliance to detect contact between a drum and tub

ABSTRACT

A method of operating a laundry treating appliance with a rotating drum located within a tub to detect contact between the drum and a tub.

BACKGROUND OF THE INVENTION

Contemporary laundry treating appliances, such as a horizontal washing machine, may be provided with a treating chamber in the form of a rotating drum received within a tub. While the drum rotates, the drum may make a physical contact with a tub, especially if the laundry in the tub is sufficiently out of balance. Continued rotation while the drum is making contact with the tub can form a hole or prematurely wear the tub. Therefore, it is desired to prevent and/or detect and then stop the drum from contacting the tub while the drum is being rotated.

SUMMARY OF THE INVENTION

A method of operating a laundry treating appliance having a rotating drum, driven by a motor, with the drum located within a tub, the method comprising the rotating the drum by driving the motor, the monitoring the mechanical drag acting on the drum and the corresponding rotational speed of the drum while the drum is being rotated, the comparing the mechanical drag to a reference mechanical drag for the corresponding rotational speed, and the determining the presence of a contact between the drum and the tub when the mechanical drag exceeds a predetermined drag threshold for the corresponding rotational speed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic, cross-sectional view of a laundry treating appliance in the form of a washing machine according to one embodiment of the invention.

FIG. 2 is a schematic view of a controller of the washing machine of FIG. 1.

FIG. 3 is a schematic, front view of a rotating object, in the form of a drum, with respect to a non-moving object, in the form of a tub, with a phantom line showing a physical contact between the drum and the tub while the drum is being rotated during a cycle of operation.

FIG. 4 is a schematic plot of the motor power usage and the rotational speed of the drum with time during constant acceleration, showing the change in the power usage with the physical contact between the drum and the tub.

FIG. 5 is a schematic plot of the motor power usage and the rotational speed of the drum with time during a constant rotational speed operation, showing the change in the power usage with the physical contact between the drum and the tub, similar to FIG. 4.

FIG. 6 is a flow chart illustrating a method for determining the physical contact between the drum and the tub while the drum is being rotated during a cycle of operation.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 is a schematic view of a laundry treating appliance 10 in the form of a horizontal axis washing machine 10 according to one embodiment of the invention. While the laundry treating appliance is illustrated as a horizontal axis washing machine 10, the laundry treating appliance according to the invention may be any appliance which treats laundry such as clothing or fabrics. Non-limiting examples of the laundry treating appliance may include a front loading/horizontal axis washing machine; a top loading/vertical axis washing machine; a combination washing machine and dryer; an automatic dryer; a tumbling or stationary refreshing/revitalizing machine; an extractor; a non-aqueous washing apparatus; and a revitalizing machine. The washing machine 10 described herein shares many features of a traditional automatic washing machine, which will not be described in detail except as necessary for a complete understanding of the invention.

Washing machines are typically categorized as either a vertical axis washing machine or a horizontal axis washing machine. As used herein, the “vertical axis” washing machine refers to a washing machine having a rotatable drum, perforate or imperforate, that holds fabric items and a clothes mover, such as an agitator, impeller, nutator, and the like within the drum. The clothes mover moves within the drum to impart mechanical energy directly to the clothes or indirectly through liquid in the drum. The liquid may include one of wash liquid and rinse liquid. The wash liquid may have at least one of water and a wash aid. Similarly, the rinse liquid may have at least one of water and a rinse aid. The clothes mover may typically be moved in a reciprocating rotational movement. In some vertical axis washing machines, the drum rotates about a vertical axis generally perpendicular to a surface that supports the washing machine. However, the rotational axis need not be vertical. The drum may rotate about an axis inclined relative to the vertical axis. As used herein, the “horizontal axis” washing machine refers to a washing machine having a rotatable drum, perforated or imperforate, that holds fabric items and washes the fabric items by rubbing against one another as the drum rotates. In some horizontal axis washing machines, the drum rotates about a horizontal axis generally parallel to a surface that supports the washing machine. However, the rotational axis need not be horizontal. The drum may rotate about an axis inclined relative to the horizontal axis. In horizontal axis washing machines, the clothes are lifted by the rotating drum and then fall in response to gravity to form a tumbling action. Mechanical energy is imparted to the clothes by the tumbling action formed by the repeated lifting and dropping of the clothes. Vertical axis and horizontal axis machines are best differentiated by the manner in which they impart mechanical energy to the fabric articles. The illustrated exemplary washing machine of FIG. 1 is a horizontal axis washing machine.

The washing machine 10 may have a cabinet 12 that includes a rotatable drum 14 defining a treating chamber 16 and which may be located within a tub 20 for receiving laundry to be treated during a cycle of operation. The rotatable drum 14 may include a plurality of perforations 22, such that liquid may flow between the tub 20 and the drum 14 through the perforations 22. The drum 14 may further include a plurality of lifters 24 disposed on an inner surface of the drum 14 with predetermined gaps between the lifters 24 to lift the laundry load received in the treating chamber 16 while the drum 14 rotates.

While the illustrated washing machine 10 includes both the tub 20 and the drum 14, with the drum 14 defining the laundry treating chamber 16, it is within the scope of the invention for the washing machine 10 to include only one receptacle, with the receptacle defining the laundry treating chamber 16 for receiving the laundry load to be treated.

A motor 26 may be directly coupled with the drive shaft 28 to rotate the drum 14 at a predetermined speed and direction. The motor 26 may be a brushless permanent magnet (BPM) motor having a stator 30 and a rotor 32. Alternately, the motor 26 may be coupled to the drum 14 through a belt and a drive shaft to rotate the drum 14, as is known in the art. Other motors, such as an induction motor or a permanent split capacitor (PSC) motor, may also be used. The motor 26 may rotate the drum 14 at various speeds in either rotational direction.

Both the tub 20 and the drum 14 may be selectively closed by a door 34. A bellows 36 couples an open face of the tub 20 with the cabinet 12, and the door 34 seals against the bellows 36 when the door 34 closes the tub 20.

A treatment dispenser 40 may be provided to the washing machine 10 to dispense a treating chemistry during a cycle of operation. As illustrated, the treatment dispenser 40 may be located in the interior of the cabinet 12 such that the treating chemistry may be dispensed to the interior of the tub 20, although other locations are also possible. The treatment dispenser 40 may include a reservoir of treating chemistry that is releasably coupled to the treatment dispenser 40, which dispenses the treating chemistry from the reservoir to the treating chamber 16. The treating chemistry may be any type of chemistry for treating laundry, and non-limiting examples include, but are not limited to detergents, surfactants, enzymes, fabric softeners, sanitizers, de-wrinklers, and chemicals for imparting desired properties to the laundry, including stain resistance, fragrance (e.g., perfumes), insect repellency, and UV protection.

The washing machine 10 may further include a liquid supply and recirculation system. Liquid, such as water, may be supplied to the washing machine 10 from a water supply 42, such as a household water supply. A supply conduit 44 may fluidly couple the water supply 42 to the tub 20 and the treatment dispenser 40. The supply conduit 44 may be provided with an inlet valve 46 for controlling the flow of liquid from the water supply 42 through the supply conduit 44 to either the tub 20 or the treatment dispenser 40.

A liquid conduit 48 may fluidly couple the treatment dispenser 40 with the tub 20. The liquid conduit 48 may couple with the tub 20 at any suitable location on the tub 20 and is shown as being coupled to a front wall of the tub 20 in FIG. 1 for exemplary purposes. The liquid that flows from the treatment dispenser 40 through the liquid conduit 48 to the tub 20 typically enters a space between the tub 20 and the drum 14 and may flow by gravity to a sump 52 formed in part by a lower portion of the tub 20. The sump 52 may also be formed by a sump conduit 54 that may fluidly couple the lower portion of the tub 20 to a pump 56. The pump 56 may direct fluid to a drain conduit 58, which may drain the liquid outside the washing machine 10, or to a recirculation conduit 60, which may terminate at a recirculation inlet 62. The recirculation inlet 62 may direct the liquid from the recirculation conduit 60 into the drum 14 or tub 20. The recirculation inlet 62 may introduce the liquid into the drum 14 or tub 20 in any suitable manner, such as by spraying, dripping, or providing a steady flow of the liquid.

The liquid supply and recirculation system may further include one or more devices for heating the liquid such as a steam generator 64 and/or a sump heater 66. The steam generator 64 may be provided to supply steam to the treating chamber 16, either directly into the drum 14 or indirectly through the tub 20 as illustrated. The inlet valve 46 may also be used to control the supply of water to the steam generator 64. The steam generator 64 is illustrated as a flow through steam generator, but may be other types, including a tank type steam generator. Alternatively, the heating element 66 may be used to heat laundry (not shown), air, the rotatable drum 14, or liquid in the tub 20 to generate steam, in place of or in addition to the steam generator 64. The steam generator 64 may be used to heat to the laundry as part of a cycle of operation, much in the same manner as heating element 66, as well as to introduce steam to treat the laundry.

Additionally, the liquid supply and recirculation system may differ from the configuration shown in FIG. 1, such as by inclusion of other valves, conduits, treatment dispensers, sensors, to control the flow of liquid through the washing machine 10 and for the introduction of more than one type of detergent/wash aid. Further, the liquid supply and recirculation system need not include the recirculation portion of the system or may include other types of recirculation systems.

A controller 70 may be provided in the cabinet 12 and communicably couple one or more components to receive an output signal from components and control the operation of the washing machine 10 to implement one or more cycles of operation, which is further described in detail with reference to FIG. 2. The controller 70 may be provided with a memory 72 and a central processing unit (CPU) 74. The memory 72 may be used for storing the control software that is executed by the CPU 74 in completing a cycle of operation using the washing machine 10 and any additional software. For example, the memory 72 may store one or more pre-programmed cycles of operation that may be selected by a user and completed by the washing machine 10. The memory 72 may also be used to store information, such as a database or look-up table, and to store data received from one or more components of the washing machine 10 that may be communicably coupled with the controller 70.

The controller 70 may be operably coupled with one or more components of the laundry treating appliance 10 for communicating with and controlling the operation of the component to complete a cycle of operation. For example, the controller 70 may be coupled with a user interface 76 for receiving user selected inputs and communicating information with the user. The user interface 76 may be provided that has operational controls such as dials, lights, knobs, levers, buttons, switches, sound device, and displays enabling the user to input commands to a controller 70 and receive information about a specific cleaning cycle from sensors (not shown) in the washing machine 10 or via input by the user through the user interface 76.

The user may enter many different types of information, including, without limitation, cycle selection and cycle parameters, such as cycle options. Any suitable cycle may be used. Non-limiting examples include, Heavy Duty, Normal, Delicates, Rinse and Spin, Sanitize, and Bio-Film Clean Out.

The controller 70 may further be operably coupled to the motor 26 for controlling at least one of the direction, rotational speed, acceleration and power consumption of the motor 26, and the treatment dispenser 40 for dispensing a treating chemistry during a cycle of operation. The controller 70 may be coupled to the steam generator 64 and the sump heater 66 to heat the liquid as required by the controller 70. The controller 70 may also be coupled to the pump 56 and inlet valve 46 for controlling the flow of liquid during a cycle of operation.

The controller 70 may further be coupled to and receive input from one or more additional sensors 82, non-limiting examples of which include: a treating chamber temperature sensor, a weight sensor, a conductivity sensor, a turbidity sensor, a position sensor, a speed sensor such as rpm sensor, a motor torque sensor or the like.

FIG. 3 illustrates the problem that the invention solves in the form of a schematic, front view of the drum 14 rotating about an axis of rotation 84 with respect to the tub 20, with a phantom line showing an excursion of the drum 14 during rotation that leads to contact between the drum 14 and the tub 20 during a cycle of operation. While there may be multiple reasons or factors for such an excursion, one of the most common reasons is non-uniformly distributed laundry in the interior of the drum 14 resulting in a corresponding imbalance that for a given rotating speed of the drum overcomes the systems, such as a suspension system, of the laundry treating appliance that are designed to prevent contact between the drum 14 and tub 20.

Excursions that are more apt to result in contact tend to happen at higher drum speeds, especially rotational speeds where the laundry is “satellized” or “plastered” within the drum. By satellized or plastered, it is meant that the centrifugal force applied to at least some of the laundry by the rotating drum is sufficient to hold the at least some of the laundry at a fixed position on the drum. The magnitude of such a force is typically equal to or greater than the force of gravity, but may vary, for example because the rotational axis 84 may at an angled to the horizontal. The greatest rotational speeds of the drum typically occur during an extraction phase, where liquid is removed from the laundry by centrifugal force. Contemporary laundry treating appliances have rotational speeds up to 1400 rpm for extraction phases when satellizing occurs at around 90 rpm, which is dependent on drum size.

The physical contact between the drum 14 and the tub 20 may not be desirable in many aspects. For example, the physical contact between the drum 14 and the tub 20 generates noise and results in the customer unsatisfaction. Alternatively, the continued physical contact may incur a mechanical wear or a hole and/or eventually leak to the tub 20, and the liquid may flow outside the tub 20. Therefore, while the drum 14 rotates, the frequency and duration of the physical contact between the drum 14 and tub 20 need to be minimized and/or eliminated such that any noise or damage including a hole or wear to the tub 20 may be prevented. The ability to sense and then eliminate the contact between the drum 14 and tub 20 has several advantages. For example, the gap between the drum 14 and the tub 20 may be configured for maximized laundry treating capacity of the laundry treating machine 10. Current laundry treating appliances have a large gap as one approach to preventing or minimizing contact. Further, the use of high-cost, wear-resistant materials for the tub 20 may be minimized and overall manufacturing cost can be lowered. And most importantly, the generation of the noise from and any mechanical wear of the laundry treating appliance 10 may be prevented.

The invention addresses the problems associated with the physical contact between the rotating object such as the drum 14 and non-moving object such as the tub 20 by monitoring the rotational speed of the drum 14 and the power consumed by the motor 26 during a cycle of operation. It has been discovered that there is a relationship between the power consumed by the motor 26 during rotation and the rotational speed of the drum 14, which can be used to determine if contact is present. When such contact is determined, then one or more actions may be taken to eliminate the contact, non-limiting examples of which are: slowing down the drum 14, redistributing the laundry, or stopping the phase and/or the entire cycle of operation.

The relationship between the power consumed by the motor 26 and drum speed is illustrated in FIG. 4, which is a schematic plot of the power consumed by the motor 26 and the rotational speed of the drum 14 with time during constant acceleration, showing different power usage with the physical contact between the drum 14 and the tub 20. As illustrated, it may be understood that, in the absence of any physical contact, practically a proportional relationship between the power and the rotational speed may be observed with respect to the time. For example, during a constant acceleration step where the rotational speed of the drum 14 linearly increases, the power consumed by the motor 26 also increases in a proportional relationship with respect to the rotational speed of the drum 14.

As illustrated, in case the physical contact between the rotating drum 14 and the tub 20 occurs, for example, around 700 rpm during the acceleration, the power consumed by the motor 26 may deviate and follow a different path than the idealized path. It is illustrated that, the power consumption, once the physical contact occurs, increases steeply for a predetermined time period, for example, for several seconds, then followed by gradual increase in the power until the rotational speed of the drum 14 reaches to a speed programmed by a cycle of operation.

As can be seen, when contact is present, the actual power consumption diverges from the non-contact power consumption for a given rotational speed. Thus, a comparison of the relationship between power consumed and rotational speed for the actual and idealized conditions may be used to determine the presence of contact.

It may be understood that the motor power may be effected by internal and/or external parameters such as the inlet voltage fluctuation or precision level of the controller 70, and, therefore, the motor power level may not be consistent, instead fluctuate within a predetermined range during the operation. Therefore, in making the comparison, it is advantageous to establish a threshold level that may be generally set above the motor power level by a predetermined amount such that the motor power fluctuation may not be confused with the physical contact, and the presence of the physical contact may be determined when the motor power jumps above the threshold level by a predetermined amount.

The divergence from idealized power consumption during contact is attributable to a portion of the energy used to rotate the drum is being transferred from the rotating drum 14 to the tub 20. The transfer of energy between two objects may be represented in a variety of forms such as light, heat or friction. Alternatively, the transfer of energy may be observed in the form of slowing down of the rotational speed of the drum 14 at corresponding power level. For example, assuming no changes in the power, the rotational speed of, for example, 700 rpm may be measured in the absence of the physical contact while slower rotational speed may be expected in case the rotating drum 14 and the tub 20 come to the physical contact. Under this condition, the controller 70 may receive the signal corresponding to the actual rotational speed of drum 14 from the sensor coupled to the drum 14 or motor 26, and may control the motor power such that the rotational speed of drum 14 may keep up with a pre-programmed drum speed within a predetermined time period. As a result, the motor power may typically increase steeply to reach to a new power, which is greater than the power corresponding to the power without any physical contact, to attain the preset rotational speed of drum within a predetermined time period.

It may be noted that the motor power consumption does not instantaneously go back to the level without the physical contact, instead, maintains the increased power level for a time period. That is, there is at least a shift or jump in the power consumption for a given speed, without a corresponding drop when contact is no longer present. It is believed that this non-responsiveness may be related with the controller 70 controlling the operation of the motor 26. At the rotational speed range of several hundred rpms, the controller 70 may not be capable of altering the rotational speed of the drum 14 before the drum 14 rotates at least several more revolutions, and the controller 70 may further provide power to the motor 26 to increase the rotational speed of the drum 14 to the pre-set speed profile. Thus, contrary to what is typically expected, the contact between the drum 14 and tub 20, which generally happens on a per/revolution basis, does not appear as such in the power consumption of the motor 26. As such, the repeated discrete or instantaneous contacts, do not show up as discrete or instantaneous spikes in the consumed power, resulting in the power signal being “blind” to the discrete or instantaneous spikes. However, it has been found that the shift in power consumption relative to an idealized power consumption for a given speed is indicative of contact even though the individual contacts may not be resolved or discernable in the power signal.

While FIG. 4 shows the change in power during an acceleration ramp, FIG. 5 is a schematic plot of the motor power usage and the rotational speed of the drum 14 with time during a constant rotational speed operation, showing the change in the power usage with the physical contact. In the absence of the physical contact, almost constant power may be required to maintain the pre-set rotational speed of the drum 14. Similar to the FIG. 4, when the physical contact occurs, the power usage may jump to a higher level and maintain at the level for a time period until the power level comes back to the level with no physical contact. Therefore, the relationship between actual power and idealized power for a given rotational speed may be used to determine the presence of contact during either an acceleration phase of the drum 14 or a constant speed phase of the drum 14. In fact, relatively small time segments of the power during the acceleration phase of the drum 14 have such small changes in speed that they can be modeled as constant speed phases for small time frames.

In either the acceleration phase or the constant speed phase, the energy transfer from the physical contact between the drum 14 and the tub 20 may be described by the following equations. We may begin with the law of conservation of energy:

ΣE _(in) =ΔE _(internai) −ΣE _(out)  (1)

Where ΣE_(in) is the energy provided to the drum 14 for drum rotation, ΔE_(internal) is the energy provided from the motor 26, and ΣE_(out) is the energy loss such as fraction and heat.

Considering energy transfer between a rotating object and non-moving object only gives the following equation:

ΣE _(in (motor)) =ΔE _(kinetic) −ΣE _((drag))  (2)

Where ΣE_(in (motor)) is internal energy of the drum 14 for rotation, ΔE_(kinetic) is the energy provided from the motor 26, and ΣE_((drag)) corresponds to the energy loss from the physical contact between the drum 14 and the tub 20.

For a system having rotational movements such as the drum rotation about an axis of rotation, kinetic energy of an rotating object may be given by:

E _(K)=½Iω ²  (3)

Where I is inertia and ω is angular frequency. For short period of time, I can be approximated as constant. Solving for the derivatives of the equation (2) gives the following relationship:

P _(mechanical in) =P _(mechanical out (drag))+Rate of change in E _(in (motor))  (4)

Where P_(mechanical in) is the power provided from the motor 26, and P_(mechanical out (drag)) is defined as mechanical drag. Assuming mass is approximated as constant, rate of change in E_(in (motor)) is expressed in rate of change in speed, V. Considering the rate of change in speed corresponds to acceleration, the rearrangement of equation (4) gives:

P _(mechanical out (drag)) =P _(mechanical in) −C·acceleration (a)  (5)

Where C is a constant.

From equation (5), it may be understood that P_(mechanical out (drag)) may depend on other parameters such as P_(mechanical in), inertia, the rotational speed, or acceleration for corresponding rotational speed of the rotating drum 14. Once the physical contact occurs, the rotational speed of the drum 14 generally decreases to a lower level than the speed where no physical contact is assumed. When the rotational speed changes, the acceleration also changes, and different acceleration value in equations (5) may result in the change of P_(mechanical out (drag)).

Real-time values for these parameters are typically available with most laundry treating appliances. For example, many laundry treating appliances have algorithms for determining the inertia of the load, with the inertia of the relevant portions of the laundry treating appliance being known. The acceleration and/or speed, from which acceleration may be determined, is normally an output of a controller of the motor 26, which may be a dedicated controller separate from the controller 70 or part of the controller 70. P_(mechanical in) is the power consumed by the motor 26, which may be determined as the torque of the motor 26, since the torque is indicative of the power. The torque of the motor 26 is typically output from the motor 26, motor controller or the controller 70, which may include the motor controller.

Therefore, monitoring P_(mechanical out (drag)) by monitoring the parameters, which are conveniently already available in most laundry treating appliances, may be one way to use power to determine if the physical contact between the drum 14 and the tub 20 occurs during a cycle of operation. The rotational speed of the drum 14 may be monitored while the drum 14 is being rotated according to a cycle of operation. The monitoring may be conducted in either continuous or non-continuous way.

Once monitored, the mechanical drag may be compared to a reference mechanical drag, such as a drag threshold, for the corresponding rotational speed that may be stored in the memory 72 of the controller 70. The drag threshold may be determined based on the threshold level, which is illustrated in FIGS. 4 and 5. For example, the drag may be configured to be proportional to the threshold level or to be higher than the threshold level by a predetermined amount. If the mechanical drag monitored jumps up or becomes significantly greater than the drag threshold by a predetermined amount for the corresponding rotational speed, it may be determined that there is the physical contact between the drum 14 and the tub 20.

Alternatively, the real-time relationship may be used in determining the physical contact between the drum 14 and the tub 20. The real-time relationship between the real-time power consumption and at least one of the rotational speed and acceleration may be compared to a threshold relationship with a reference power. If the real-time power consumed is greater than the reference power by a predetermined amount, it is determined that the contact between the drum 14 and the tub 20 present.

FIG. 6 illustrates a method 600 for determining the physical contact between the drum 14 and the tub 20 while the drum 14 is being rotated during a cycle of operation. It is noted that the sequence of steps depicted in FIG. 6 is for illustrative purposes only, and is not meant to limit the method in any way as it is understood that the steps may proceed in a different logical order, additional or intervening steps may be included, or described steps may be divided into multiple steps, without detracting from the invention. The method may be incorporated into a cycle of operation for the laundry treating appliance 10, such as prior to or as part of any phase of the treatment cycle. The method may also be a stand-alone cycle.

The method 600 assumes that the laundry may be received in the drum 14 before, during, or after a cycle of operation. At 602, the drum 14 may rotate in accordance with a cycle of operation. The rotational speed of the drum 14 may be configured to accelerate or maintain to be constant. At 604, the mechanical drag may be monitored by monitoring the power or other parameters such as motor torque. The rotational speed of the drum 14 may be also monitored.

At 606, the mechanical drag may be compared to the drag threshold. In case the mechanical drag is greater than the drag threshold, it may be determined that there is a contact between the drum 14 and the tub 20, as illustrated in 608.

While the method of monitoring the mechanical drag and the corresponding rotational speed of the drum 14 and comparing the mechanical drag to a reference mechanical drag may be applicable for all range of rotational speed, it may be noted that the comparing to a reference mechanical drag may be especially beneficial for rotational speeds above the satellizing speed. The method is especially useful at higher rotational speeds associated with extraction, such as 500 rpm and above for the illustrated laundry treating appliance. It may be noted that the rotational speed of 500 rpm is not a fixed speed, and may depend on the configuration of the laundry treating appliance 10.

It may be understood that the mechanical drag may be more clearly observed in the high rotational speed range than in the low rotational speed range. The possible consequences of the mechanical drag, such as tub wear or hole may become significant in the high rotational speed range, especially above the satellizing speed, which may make the invention very suitable for the high rotational speed range.

The controller 70 for controlling the motor 26 may be configured such that, at rotational speeds above the satellizing speed, the rotational speed of the drum 14 cannot be substantially and immediately changed without passing of several revolutions of the drum 14. Further, due to the nature of high speed revolution of the drum 14, it may not be practical to look for abrupt change in either the increase in the power consumed or the decrease in the rotational speed of the drum 14 which corresponds to the physical contact as these abrupt changes are not typically discernable in the signals from the typical sensors such as a speed sensor or a rpm sensor. Instead, the physical contact may be determined simply by monitoring the mechanical drag at high rotational speeds, without using typical sensors.

The invention described herein provides methods for detecting the physical contact between the rotating object such as drum 14 and the non-moving object such as tub 20. The methods of the invention can be advantageously used in preventing the damage such as hole or wear to the tub from impact by the rotating drum 14. By detecting the physical contact in a controlled way, the gap between the drum 14 and the tub 20 may be designed to manufacture a laundry treating appliance with maximized laundry treating capability that requires minimum installation space while the use of high cost, wear-resistant tub material is minimized.

While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation. Reasonable variation and modification are possible within the scope of the forgoing disclosure and drawings without departing from the spirit of the invention which is defined in the appended claims. 

1. A method of operating a laundry treating appliance having a rotating drum, driven by a motor, with the drum located within a tub, the method comprising: rotating the drum by driving the motor; monitoring the mechanical drag acting on the drum and the corresponding rotational speed of the drum while the drum is being rotated; comparing the mechanical drag to a reference mechanical drag for the corresponding rotational speed; and determining the presence of a contact between the drum and the tub when the mechanical drag exceeds a predetermined drag threshold for the corresponding rotational speed.
 2. The method of claim 1 wherein driving the motor comprises providing the motor with an acceleration rate.
 3. The method of claim 1 wherein the monitoring is non-continuous.
 4. The method of claim 3 wherein the monitoring is done at a predetermined sampling rate.
 5. The method of claim 1 wherein the comparison is done when the rotational speed exceeds a reference speed.
 6. The method of claim 5 wherein the reference speed is greater than a satellizing speed.
 7. The method of claim 6 wherein the reference speed is greater than 500 rpm.
 8. The method of claim 1 wherein the presence of a contact between the drum and the tub is determined when the mechanical drag exceeds the predetermined drag threshold by a predetermined amount.
 9. The method of claim 1 wherein the mechanical drag is determined by monitoring a relationship between power consumed by the motor, an inertia, and an acceleration of the drum.
 10. A method of operating a laundry treating appliance having a rotating drum, driven by a motor, with the drum located within a tub, the method comprising: accelerating rotational speed of the drum by driving the motor; monitoring at least one of drum acceleration, drum speed and power consumed by the motor; defining a real-time relationship between the power consumed and at least one of the acceleration and speed; comparing the real-time relationship to a threshold relationship; and determining the presence of a contact between the drum and the tub when the real-time relationship satisfies the threshold relationship.
 11. The method of claim 10 wherein driving the motor comprises providing the motor with an acceleration rate.
 12. The method of claim 10 wherein the monitoring is non-continuous.
 13. The method of claim 12 wherein the monitoring is done at a predetermined sampling rate.
 14. The method of claim 10 wherein the comparison is done when the rotational speed exceeds a reference speed.
 15. The method of claim 14 wherein the reference speed is greater than a satellizing speed.
 16. The method of claim 15 wherein the reference speed is greater than 500 rpm.
 17. The method of claim 10 wherein the real-time relationship satisfies the threshold relationship when the real-time power consumed is greater than a reference power for reference relationship.
 18. The method of claim 17 wherein the real-time relationship satisfies the threshold relationship when the real-time power consumed is greater than the reference power by a predetermined amount. 